National Academies Press: OpenBook

Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories (2009)

Chapter: Chapter 1 - Introduction and Background

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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 1 - Introduction and Background." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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1This Guidebook is intended to provide concise instruc- tions primarily to airport operators on how to develop an airport-specific greenhouse gas (GHG) emissions inventory. Instructions are provided to guide the user in developing ap- propriate and consistent inventories. Rather than burden the body of the Guidebook with too much detail, much of the de- tailed background information supporting the suggestions in the Guidebook is provided in the appendices that serve as a companion to the Guidebook. Every attempt has been made to keep the Guidebook simple to use and, thus, the Guidebook relies on the appendices for greater elaboration and support for the methods. Many airport operators prepare an air quality protocol before embarking on the development of an inven- tory (protocols refer to documents that identify data sources and methodologies to be deployed in an analysis.). This Guide- book is not intended to replace such protocols, but rather serve as a reference point for various methods. With clarity and conciseness in mind, the Guidebook is organized to provide first a brief introduction and limited background information in this chapter (Chapter 1). The chapter reviews issues associated with airport GHG inven- tories which the user should consider before embarking on preparing an inventory. Then Chapter 2 provides directions for developing inventories, covering the protocols neces- sary for properly setting up an inventory. This is followed by instructions in Chapter 3 on how to calculate emissions from each source and how to create carbon dioxide (CO2) equivalencies. the calculation methods in Chapter 3. The overall procedure for developing an inventory is shown in Figure 1-1. First-time users of this Guidebook should follow each of the steps shown in Figure 1-1 to become accustomed to the theories and materials in each chapter. After that, Step 2 (Chapter 2) could essentially be the starting point. 1.1 Purpose of the Guidebook Currently, the United States has no national or state leg- islative mandates for an airport operator to prepare GHG emissions inventories. Generally, the few inventories that have been generated by or for airports have been done vol- untarily, even though they may be based on requests from municipalities. Such voluntary actions have been conducted in response to state and local climate action initiatives or, in the case of two inventories (for airport improvements at Sacramento International Airport and San Diego Interna- tional Airport), were prepared in response to the California Environmental Quality Act (CEQA) analysis of proposed air- port improvements. With no national legislative mandates, there is also no clear guidance on developing airport-specific inventories. As is shown in Appendix F of this report, airport GHG inventories differ in their approaches. To fill this need, TRB initiated Project 02-06 under the Airport Cooperative Research Program (ACRP) to develop this Guidebook for airports. The purpose of the Guidebook is to provide consistent guidance on developing airport GHG emissions inventories for those airports that wish to pre- pare such inventories. The Guidebook includes methodical instructions and diagrams to clearly specify the procedures C H A P T E R 1 Introduction and Background Chapter 2 represents the heart of the inventory development process as it provides key considera- tions for the inventory makeup. First-time users of this Guidebook should follow each of the steps shown in Figure 1-1 to become accustomed to the theories and materials in each chapter. Chapter 2 represents the heart of this Guidebook since it ties together the background information in Chapter 1 and

While the Kyoto target included domestic air travel- related emissions, emissions from international aviation were specifically excluded from the targets agreed upon under the Kyoto Protocol. Instead, countries were encouraged to con- trol international aviation-related emissions through the ac- tivities of the International Civil Aviation Organization (ICAO). ICAO’s Committee on Aviation Environmental Protection (CAEP) continues to consider the potential for using market-based mechanisms and has formed the Group on International Aviation and Climate Change (GIACC) to develop an aggressive program on international aviation and climate change. The United States has not ratified the Kyoto Protocol and has yet to develop federal legislation to regulate GHG emis- sions. In lieu of federal legislative mandates, various U.S. cor- porations, nonprofits, and local governments have engaged in largely voluntary measures to quantify and reduce GHG emissions. This includes U.S. efforts such as the Mayors Cli- mate Protection Agreement to promote the goals of the Kyoto Protocol, and the establishment of regional and national registries, such as The Climate Registry (TCR), to provide a formalized voluntary mechanism for developing, submitting, and tracking of corporate-based GHG emissions. to develop such inventories and explanations for the use of certain methods and metrics. In addition, the Guidebook is intended to provide background reasons for the development of these inventories, including the potential benefits thereof. Both the scientific understanding and policies to address climate change are quickly evolving. Thus, certain parts of this Guidebook may need to be updated in the future to reflect changes in the understanding of the impacts of emissions on climate or as improved methods to calculate those emissions become available. Further, as future regulations and proto- cols are enacted, the Guidebook will need to be updated to ac- count for these changes. Thus, the Guidebook represents a liv- ing document that is expected to be updated periodically. 1.2 Regulatory Considerations On an international level, the driving force behind the con- trol of GHG emissions has been the Kyoto Protocol (UN 1998) and local action. The protocol is a supplementary agreement to the United Nations Framework Convention on Climate Change (UNFCCC). Negotiated in Japan in 1997, the proto- col came into full force on February 16, 2005, 90 days after the ratification of at least 55 countries that represented at least 55% of 1990 global CO2 emission levels. As of February 4, 2008, 176 parties (175 countries and the European Economic Community [EEC]) had ratified the protocol. Countries that ratify the Kyoto Protocol commit to reduce their emissions of CO2 and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases. 2 The Kyoto Protocol is one of the underlying drivers for the development of airport GHG emissions inventories. Step 2 Inventory Development Considerations Chapter 1 Chapter 2 Chapter 3 Chapter 3 Step 1 Review Background Information Step 3 Calculate Emissions Step 4 Calculate CO2 Equivalencies Figure 1-1. Overall procedure for developing an airport GHG emissions inventory. In lieu of a national program to quantify and control emissions, regional and local initiatives have been developed. In addition to these voluntary actions, some state and local legislative measures have been enacted requiring inventories and establishing emission reduction goals. The most significant of these legislative mandates is the California Global Warming Solutions Act, which is also known as Assembly Bill 32 (AB32). Passed in 2006, it charges the California Air Resources Board (CARB) with developing a comprehensive GHG emissions reduction plan for California through 2020. It is the first law in the United States to cap emission levels from major indus- tries, as well as to require certain facilities to report their emis- sions, which, in this case, are reported to the California Cli- mate Action Registry (CCAR). To reinforce their climate action plans, several states have a state-based law similar to the National Environmental Policy Act (NEPA)—sometimes called mini-NEPAs—that now requires the preparation of GHG inventories. The

Massachusetts Environmental Policy Act (MEPA) requires preparation of a CO2 emissions inventory, and in King County Washington, under Washington’s State Environmental Pol- icy Act (SEPA), county-based projects are required to prepare a GHG inventory. There have been emerging discussions about federal GHG regulation following the recent U.S. Supreme Court case of Massachusetts v. USEPA. On April 2, 2007, the Supreme Court ruled on a 5-to-4 vote that USEPA has the authority to regu- late GHG emissions and that USEPA must reevaluate its stance in not choosing to do so thus far. Other efforts include the 2008 lawsuit by California to regulate GHG emissions from mobile sources and California’s petition of USEPA to regu- late industrial GHG emissions. As such, the USEPA has been under increasing pressure to regulate GHG emissions under the Clean Air Act (CAA). This Guideline has been prepared to aid airports that wish to voluntarily prepare airport-specific inventories, as well as those that may be required by existing and future mandates. 1.3 Overview of Greenhouse Gas Emissions This Guidebook focuses on the development of inventories for the following GHGs: 1. Carbon dioxide (CO2), 2. Methane (CH4), 3. Nitrous oxide (N2O), 4. Sulfur hexafluoride (SF6), 5. Hydrofluorocarbons (HFC), and 6. Perfluorocarbons (PFC). with the use of refrigeration and fire extinguishers, but these emissions are not well documented. Of the three remaining gases, emissions of CO2 at an airport tend to be better under- stood than N2O and CH4. In addition to the direct emissions, consideration can often be given to the other following pollutants that have the po- tential to exert climate change effects: water vapor (H2O), par- ticulate matter (PM), sulfur oxides (SOx), oxides of nitrogen (NOx), carbon monoxide (CO), and nonmethane volatile or- ganic compounds (NMVOC). These pollutants can produce some direct effects, but their main contributions are as pre- cursors for indirect effects. The direct effects that H2O exert tend to be dominated by the normal, natural hydrologic cycle (rainfall, evaporation, etc.). However, water vapor still may have an important effect, es- pecially for direct emissions into the stratosphere as occur for some aircraft flights. Similarly, the effects produced by PM species (i.e., black carbon or soot and sulfate aerosols) can be important. SOx adds to this effect since it can react in the atmosphere and form sulfate aerosols. Both H2O and PM also have indirect effects through contrail formation. Ozone (O3) also has a climate change effect but is not directly emit- ted. Rather, O3 is produced in the troposphere through reac- tions involving NOx or CO and NMVOCs. In the stratosphere, it is produced through a reaction involving oxygen molecules (O2) and ultraviolet (UV) radiation. Since O3 is not directly emitted, it cannot be included in an airport emissions inven- tory. However, its precursors, NOx, CO, and NMVOC can be included. NOx can also produce nitrate aerosols, thus further complicating the assessment of indirect effects. Although the indirect effects are generally considered im- portant, they also have the largest uncertainties associated with their climate impacts. Inclusion of these precursor emis- sions within a GHG inventory arguably helps to comprehen- sively capture all of the emissions related to climate change, consistent with the general guidelines specified by the IPCC in promoting the need to quantify even indirect emissions as part of the overall GHG inventory (IPCC 2006). However, since there are technical issues for these precursors, such as no well-established CO2 equivalencies for these precursors, these emissions cannot be directly compared to each other at this time using simple multipliers. More complex climate models are required for this purpose. 1.4 Overview of Reasons for Preparing Greenhouse Gas Emissions Inventories Each year, USEPA prepares a GHG inventory for the United States (USEPAb 2008). Even though the inventory is devel- oped using a “bottom-up” approach (i.e., it reflects the assess- ment of individual sectors), the sectoral data are large-scale 3 Chapter 2 discusses different levels of evaluation based on the pollutants considered. This Guide- book recommends that airport GHG inventories consider the six Kyoto pollutants (Level 2). See Section 2.3. This list mirrors the gases regulated under the Kyoto Pro- tocol. These gases are typically covered in most GHG emis- sions reporting protocols including the guidelines from the Intergovernmental Panel on Climate Change (IPCC) and the recent protocol from TCR (IPCC 1999 and TCR 2008a). For U.S. economic sectors as a whole, these gases generally repre- sent the most notable GHGs based on a combination of the quantity of pollutant emitted and potential for exerting cli- mate change effects. For aviation, emissions of the fluorinated compounds (including HFC and PFC) are less significant be- cause these compounds are generally emitted from industrial activities. They can be emitted from airport activities associated

and not specific to local (e.g., airport) sources. To aid with the national inventory, USEPA has developed GHG guidance to the states for the preparation of inventories based on a “top-down” approach and commented that such inventories “. . . may not be appropriate for use at a scale other than the state level . . .” (USEPAh 2007) Simultaneously, local juris- dictions (counties, cities, and individual airport operators) are beginning to prepare GHG inventories, and without a standard protocol for use at these smaller scales, these inven- tories cannot be compared with one another. When beginning to develop a GHG inventory, considera- tion must be given to the purpose for preparing the inven- tory. The purpose will likely dictate the sources to be evaluated and data that are available. Although there are numerous reasons why an airport operator might prepare an inventory, generally, these reasons can be grouped into the following four categories: 1. Climate change initiatives—GHG reduction goals (climate action plan), 2. Environmental management and sustainability programs (sustainability project plan), 3. Disclosure of project/action effects (regulatory-based proj- ect plan), and 4. Future regulations. The few GHG airport inventories that have been developed to date appear to fall under these categories, which are pre- sented in Appendix A. The general relationship among these different inventory purposes is shown by source coverage in Figure 1-2. It is important to note that these categories are intended to distinguish among possible types of inventories and the sources they might consider. Individual inventories prepared subject to these local programs may vary, and could overlap substantially. As shown in Figure 1-2, an inventory developed for a climate action plan or climate change initiative comprehensively in- cludes all sources while other inventories may be subsets of these same sources. The following sections provide a brief overview of these inventory reasons and their needs. 1.4.1 Climate Change Initiatives— Greenhouse Gas Reduction Goals Most often, inventories developed as part of climate change initiatives are used to identify sources of emissions, recognize their contribution to regional, state, local, or national inven- tories, and then form the basis for examining ways to reduce emissions. Included in this category are inventories prepared for purposes of climate action registries, such as TCR, the California Climate Action Registry (CCAR), and the Eastern Climate Registry (ECR). The following general characteristics are typical of inventories performed in response to climate action initiatives: • Currently voluntary—In future years it is expected that the USEPA will establish a required emissions reporting process that would fall into this category. Several city, county, re- gional, and state action plans are encouraging submission of the inventories to a climate action registry. • Typically the most inclusive of sources and their emissions of all of the inventories—Generally, inventories are segre- gated by ownership and control of the source (see Section 2.2 regarding ownership and control inventory boundaries). • Typically begin with an inventory for current-year emissions—for those whose plan includes a reduction goal, they often identify a backcast base-year’s emissions (prior year such as 1990, 2000, or 2005) and emissions in a forecast year (the year associated with the goal). It should be noted that care must be taken when backcasting and/or forecasting since the data (e.g., source activities, emission factors, etc.) to support these processes may not be very accurate. Table 1-1 provides a framework for the structure of a cli- mate action plan inventory to enable a comparison to other inventories. It is important to note that for airport operators who are submitting their inventory to a climate action registry, reg- istries have specific reporting requirements. As noted in Appendix E, the registries typically ask for emissions sources to be reported as direct (Scope 1), indirect (Scope 2), and op- tional (Scope 3). The above format would translate emissions into the registry categories in the following way: • Scope 1/direct emissions include airport operator emissions associated with (1.) fuel necessary to power airport-owned on- and off-road vehicles and (2.) direct energy necessary to power airport facilities (i.e., natural gas, fuel oil). • Scope 2/indirect emissions include purchased electricity. 4 Regulatory-Based Project Plan Sustainability Project Plan Climate Action Plan Figure 1-2. Relationship showing source coverage by different inventory purposes.

• Scope 3/indirect and optional emissions include (1.) tenant emissions, (2.) public ground travel on- and off-airport, and (3.) airport employee commute emissions. Table 1-2 provides a sample inventory format of an inven- tory created for climate registry purposes that might be pre- pared for an airport using the Scope 1, 2, and 3 categories. Climate action registries also seek the reporting of the following three primary GHGs: carbon dioxide (CO2), nitrous oxides (N2O), and methane (CH4). There are differing opin- ions as to how to create CO2 equivalencies (CO2e is a metric used to compare the emissions of different GHGs based upon their global warming potential, which is used to convert GHGs to CO2 equivalents.) It is recommended that global warming potentials (GWPs) from the latest IPCC assessment report (at this time, the Fourth Assessment Report) be used to calcu- late CO2e (IPCC 2007). However, to maintain consistency with previous inventories or to maintain consistency with other inventory development protocols such as those from the CCAR, TCR, and the International Council for Local Environ- mental Initiatives (ICLEI), whether or not mandated by gov- ernment or other organizations, GWPs from previous IPCC assessment reports (e.g., Second Assessment Report and Third Assessment Report) can be used. This Guidebook recom- mends that the documentation accompanying the inven- tory note which assessment is used and present the original mass emissions by pollutant prior to the application of the GWP, as well as the resultant CO2e values. 5 This Guidebook recommends use of GWPs from the latest IPCC assessment report (at this time, the Fourth Assessment Report), noting the source of the GWPs, presenting the original mass emissions by pollutant prior to the application of the GWPs, as well as the results after application. User/Source Category Scope CO 2 (metric tons/year) Percent of Source in Use r Category Percent of Total Airport Operator Owned/Controlled Stationary/facilities – purchased facility power 2 30,000 51.7% 1.2% Stationary/facilities – natural gas 1 10,000 17.2% 0.4% Ground support equipm ent/airport fleet 1 3 ,000 5.2% 0.1% Ground access vehicles (public vehicles on airport roads)* 3 15,000 25.9% 0.6% Total Airport Operator Owned/Controlled 58,000 100% 2.3% Airline, Aircraft Operator, or Tenant Owned/Controlled Aircraft 3 Ground 3 140,000 6.2% 5.5% Ground to 3,000 ft 3 207,000 9.2% 8.1% Above 3,000 ft (residual/cruise/APU) 3 1 ,890,000 84.1% 74.1% Aircraft Total 3 2 ,237,000 99.5% 87.7% Ground support equipment 3 6 ,540 0.3% 0.3% Ground access vehicles 3 1 ,270 0.1% 0.1% Stationary sources/facility power 3 3 ,000 0.1% 0.1% Total Airline, Aircraft Operator, or Tenant Owned/Controlled 2,247,810 100% 88.2% Public Owned/Controlled Public vehicles 3 175,000 71.72% 6.9% Taxis 3 34,000 13.93% 1.3% Vans/shuttles 3 23,000 9.43% 0.9% Light rail 3 U nknown na na Cargo trucks 3 12,000 4.92% 0.5% Total Public Owned/Controlled 244,000 100% 9.6% Total 2,549,810 100% Waste recy cling 3 ( 852) Grand Total Emissions 2,548,958 *For purposes of this inventory reporting format, on-airport roadway vehicular travel-related emissions (both the emissions of/from the airport operator vehicles as well as public travel) are identified as airport operator controlled, as this infrastructure is owned and could be controlled by the airport operator. Thus, for the expanded reporting format, these sources are listed in the airport-controlled category, but are noted as Scope 3 to maintain consistency with TCR reporting formats. Table 1-1. Sample climate action plan emissions inventory.

1.4.2 Environmental Management and Sustainability Programs Airport operators that have adopted sustainability practices may wish to quantify GHG emission reduction benefits associ- ated with their sustainability practices. For these inventories, the Guidebook strives to suggest the greatest flexibility in presenting data. A sustainability plan typically identifies individual actions that an airport operator is taking and/or plans to take to reduce its environmental footprint. In this case, the focus may be on the airport as a whole or it may be on individual projects. For the case where the desire is to inventory the airport in its en- tirety, the previously defined approach for climate change ini- tiatives may be used. In the case of individual sustainability projects, only the sources that are affected by the action might be inventoried. For example, if an airport installed precondi- tioned air and 400-hz power at the gates, the emission reduc- tion benefits associated with aircraft using these systems might be contrasted with the emissions associated with aircraft con- tinuing to use their auxiliary power units (APUs). Table 1-3 provides an example of the results of a sustainability project. 6 Emission Source 2006 Emissions (CO2e in metric tons) Direct/Scope 1 Stationary/facilities—natural gas 10,000 Ground support equipment/airport fleet 3,000 Subtotal, Direct/Scope 1 13,000 Indirect/Scope 2 Purchased electricity (airport owned/controlled) 30,000 Subtotal, Indirect/Scope 2 30,000 Optional/Scope 3 Aircraft/APU 2,237,000 Tenant ground support equipment 6,540 Tenant ground access vehicles 1,270 Tenant stationary sources/facility power 3,000 Public vehicles (off-airport travel) 175,000 Taxis (off-airport travel) 34,000 Vans/shuttles (off-airport travel) 23,000 Light rail (off-airport travel) unknown Cargo trucks (off-airport travel) 12,000 Ground access vehicles (public vehicles on airport roads) 15,000 Subtotal, Optional/Scope 3 2,506,810 Total 2,549,810 Waste Recycling (852) Grand Total 2,548,958 Table 1-2. Sample climate action plan emissions inventory—registry reporting format. Projects in a sustainability program aim to reduce the environmental footprint of the airport, and the resulting inventory may be a subset of that which would be prepared for a Climate Action Inventory. Inventories developed under the project disclo- sure umbrella are mainly related to the NEPA (or state NEPA-like) process where an agency ap- proval is involved, and—as a result—the inventory reflects only the changes in emissions due to the project and is a subset of the Climate Action In- ventory. Only a subset of the sources (i.e., those affected by the project) are included in a project disclosure inventory. It is anticipated that as planning progresses at airports and more sustainability plans are developed and implemented, air- port operators are likely to include the quantification of GHGs as part of their plans from the tactical perspective (the emis- sion changes associated with actions) and also in a strategic sense (how future plans and policies may affect climate action goals as well as the effects of climate change on airports). In quantifying emissions associated with a sustainability plan, the airport operator would have flexibility in how GHGs are presented. For those plans that include more than CO2, this Guidebook recommends developing CO2 equivalencies using the same approach as is used for climate action plans. 1.4.3 Disclosure of Project/Action Effects Annual Metric Tons of CO2 Source No Action With Sustainability Action Effect of the Sustainability Action APU 15,000 7,000 (8,000) Facility power emissions 30,000 35,000 5,000 Total 45,000 42,000 (3,000)(Emissions Reduced) Table 1-3. Example emissions quantification of a sustainability project. Inventories may also be required to support actions involv- ing state and, possibly, federal approvals of airport improve- ments. In the United States, this project/action disclosure could occur in the form of documents prepared under NEPA

or based on state requirements that are similar to NEPA (called state NEPA-like laws or mini-NEPAs). As noted in Appendix A, there is currently no requirement to consider GHGs in NEPA, but several state NEPA-like processes are now requiring such evaluations. A NEPA or state NEPA-like evaluation focuses on the project-related effects of an agency action. As has been the case of air quality assessments for criteria pollutants (CO, N2O, etc.), consideration is limited to the air quality emission inventories associated with the sources that are affected by the action. For example, if the proposed action is a development project that would extend a runway, only the sources that would be affected by that action (the runway extension) would be inventoried. The primary analysis function of NEPA is to identify and disclose the effect of the project rela- tive to what would happen if the project was not undertaken. In the runway extension example, the analysis might only focus on aircraft taxi movements and construction emissions. To support that analysis, documentation would be necessary to show how the project would affect existing and future air- craft operations levels (e.g., additional flights that may be induced). If additional flights would be induced, then addi- tional support activity might occur, requiring the considera- tion of other sources. Using this example, assuming that the runway extension would not induce activity relative to the no-action alterna- tive, the project could affect energy use relative to sources owned and controlled by the airport operator, as well as its airport tenants. Each source and each owner should be con- sidered. For instance, a slight increase in a subset of facilities/ stationary sources could occur due to additional runway lights, and the construction process would consume energy and generate GHGs. Once the project is complete, it is likely that the runway extension would alter taxi-related aircraft emissions (reflected in the aircraft-ground category). Sum- ming together the sources of emissions under various owner- ship and control would result in a net emission change and be reflected as a reduction, as shown in Table 1-4. As noted in Appendix A, no specific guidance has been de- veloped for NEPA-related GHGs. The inventories prepared to date for airports in California, subject to California’s NEPA- like law (CEQA), have reflected three primary gases (CO2, N2O, and CH4). In Massachusetts, the state NEPA-like law only requires the consideration of CO2, except in specific circum- stances where other pollutants are known to be substantial. For project disclosure airport inventories, the three primary GHG pollutants should be presented, and the GWPs as discussed for climate change initiatives/action plans should be used. 7 Annual CO2 Emissions (metric tons) User/Source Category No Action Runway Extension Preferred Alternative Net Post Project- Related Emissions Airport Operator Owned/Controlled Sources Affected Facilities/stationary sources (airfield lighting for the runway) 40 41 1 Ground support equipment (vehicles needed to support construction of the runway) 0 220 220 Total Airport Operator Owned/Controlled Affected 40 261 221 Airline, Aircraft Operator, or Tenant Owned/Controlled Aircraft Ground 140,000 138,700 -1,300 Ground to 3,000 ft NA NA 0 Above 3,000 ft NA NA 0 Aircraft Total 140,000 138,700 -1,300 APU NA NA 0 Ground support equipment NA NA 0 Ground access vehicles NA NA 0 Stationary sources NA NA 0 Total Airline, Aircraft Operator, or Tenant Owned/Controlled 140,000 138,700 -1,300 Public Owned/Controlled Public vehicles NA NA 0 Shuttles and private vehicles NA NA 0 Total Public Owned/Controlled NA NA 0 Total Metric Tons Project Affected Sources 140,040 138,961 -1,079 Notes: For some sources, only the sources of emissions that would be affected by the project are quantified. NA = Project would not affect emissions from this source and thus emissions are not assessed. Table 1-4. Example inventory—disclosure of project effects.

1.4.4 Future Regulations Appendix A notes a number of initiatives that are under- way that could lead to regulation and/or the required report- ing of GHGs. At this time, it is not possible to estimate the specific format and requirements of such regulation. It is pos- sible that a unique reporting protocol might be necessary. However, it is also likely that one of the earlier formats would also serve those needs. Perhaps the single most important regulation that could be enacted would come from USEPA. A national mandate to track and reduce GHG emissions could have far-reaching im- plications on all aspects of developing GHG inventories for airports. The recent lawsuits against USEPA by Massachusetts and California provide some indications of the pressures placed on USEPA to develop legislation. and better satisfaction of those regulations. Based on the specifics of each regulation and the needs of the airport op- erator, the inventories could be similar to those developed as part of a climate action plan or a subset corresponding to specific projects. In addition to, or as part of, the GHG emissions tracking work, an airport could potentially position itself to gener- ate revenues through carbon trading. As the carbon trading market becomes more established than it is currently, airports may be able to take advantage of the opportunities. 1.5 Airport Source Contributions to Greenhouse Gas Emissions Aviation is just one mode of transportation that, in turn, is just one of many GHG emitting sectors. As shown in Fig- ure 1-3, in the United States, the transportation sector is the second largest emitter of GHGs; the first is electricity gener- ation (USEPAa 2007). Within the transportation sector, ground vehicles (e.g., auto- mobiles and trucks) comprise most of the GHG emissions, as indicated in Figure 1-4. 8 An inventory developed in anticipation of future regulations may be as comprehensive as one de- veloped for a climate action plan or a subset, and it would help the airport be better prepared for the regulations. "U.S. Territories" (Other sources) 1% Commercial 4% Residential 6% Industrial 15% Electricity Generation 41% Transportation 33% (Source: EPAa 2007) Figure 1-3. U.S. GHG emissions by sector. An inventory developed in anticipation of future regula- tions would allow an airport operator to be better prepared to handle any actual regulations that are enacted. The in- ventory would allow better tracking of emissions over time, Aviation accounts for 11% of transportation GHG emissions and is the only source that emits directly into the higher levels of the atmosphere.

Commercial aviation accounts for about 11% of GHG emis- sions from transportation sources, or about 3% of total emis- sions, and represents the third largest source of transportation GHG emissions (behind automobiles and personal trucks). For aircraft emissions, the FAA indicates on a mass basis, emissions are “composed of about 70% CO2, a little less than 30% H2O, and less than 1% each of NOx, CO, SOx, VOC, PM, and other trace components including HAPs.” Most of the emissions are emitted during “cruise” (above 3,000 ft [914.4 m]) including about 90% of the CO2 emitted and 70% of the CO emitted (FAAa 2005, p. 1). Globally, between 18% to 44% of aircraft emissions are emitted in the stratosphere (Gettelman & Baughcum 1999). 1.6 Introduction to the Use of Equivalency Methods A significant dilemma in the evaluation of GHGs, particu- larly those associated with aviation, is how to account for the effects of the wide range of individual GHGs that are emitted. Different chemical species emitted from human and natural sources have different impacts on climate. For example, one ton of CO2 has a different effect on the climate than one ton of methane (CH4), and these effects occur over different periods of time. Further, some of these species have different impacts depending on where they are emitted (latitude, longitude, and altitude), when they are emitted (both time of day and time of year), what other chemicals are present in the atmosphere (from other natural and man-made sources), and on both local and long-term weather trends. Scientists use complex computer simulations to approxi- mate the physics and chemistry of these different effects. These simulations may take days or months to run. The most comprehensive reviews of the results of these complex simu- lations, of the measured data regarding climate change, and of the effects of different natural and human sources, are those provided by the IPCC, an international group of scien- tists brought together under the umbrella of the UN (see, for example, the most recent climate assessments in IPCC 2007). Using results from these complex computer simulations, scientists have developed simplified methods for estimating the relative impacts on climate change of different chemical species and sources (e.g., different modes of transportation, home heating, cement making, etc.). These methods for re- lating impacts are called equivalency methods. They all require additional approximations and assumptions (beyond those in the more complex climate models), and may implicitly or explicitly incorporate economic and moral or value-based as- sumptions (e.g., the relative importance of effects that occur 20 years from now versus effects that occur 100 years from now). It is important to recognize that such scientific ap- proximations, and economic and value-based assumptions, are required for analyzing trade-offs and relative contribu- tions to climate impact. There is no way to avoid these issues. Further, the implicit assumptions are sometimes not obvious for various equivalency methods. Therefore, it is critical that the underlying assumptions be clearly understood and docu- mented when using such equivalency methods. Because of the high degree of uncertainty in estimating the impacts of some chemical species (especially those with 9 Automobiles 56% Personal Truck 28% Transit Buses 1% Commercial Airlines 11% Intercity Rail (Amtrak) <1% Transit Rail <1% Commuter Rail <1% Other (motorcycles, recreational boats, general aviation, intercity and school buses) 4% (Source: FAAa 2005) Figure 1-4. U.S. transportation sector GHG emissions by mode.

complex indirect effects), and the different moral and value- based assumptions that may be implicit in these methods, there is a healthy scientific debate regarding the “best” equivalency methods. Scientists, economists, and others who study climate recognize that the usefulness of different equivalency methods often depends on the question one asks and the way in which the equivalent emissions are judged. scenarios are required to estimate the relative effects of the emissions. A simple multiplier is generally not appropriate. As already noted, depending on the policy question, dif- ferent equivalency methods may be more or less appropriate. Further, the scientific understanding of some effects is still relatively immature, and both the equivalency methods and the specific equivalency values are likely to change over time. Nonetheless, equivalency methods are useful for taking action based upon the compiled inventories or, in some cases, for summing up the overall magnitude of several different species (e.g., in a CO2e unit). For purposes of creating a CO2e, it is recommended that the latest IPCC Fourth Assessment Report (IPCC 2007) be used and noted in the documentation of the emissions inventories. Sep- arately accounting for each pollutant and reporting their emis- sions alongside the GWP values (while noting the source of the GWPs) would allow adjustments in the future as refined GWP values become available (e.g., from future IPCC assessment re- ports). Section 3.8 presents the specific process for calculating CO2e. Although the GWPs from the Fourth Assessment Report are recommended, GWPs from prior reports can be used for consistency with previous inventories and other existing pro- tocols. In general, it is recommended that a GHG inventory should always include both the original mass quantities of each pollutant as well as the CO2e masses. This allows comparisons of the different pollutants as well as for potential changes to the CO2e values if improved GWPs become available. 1.7 Allocating Emissions Reductions A dilemma that airport operators are likely to have in the future quantification of emissions is how to allocate emis- sion reductions that the airport operator has implemented or funded through various funding sources (rates and charges, grants, bonds, etc.) that result in emission reduc- tions associated with a source that is owned and controlled by another party (i.e., tenants or public ground travel to/ from the airport). For purposes of this section, those actions are referred to as actions where the airport operator has “in- fluence,” but does not own the source or control the emis- sions (see Section 2.2 for ownership and control inventory boundaries). There are numerous instances where one party may have influenced the emissions of another party’s sources. These influences represent actions that have the potential to shift emissions from one party to another. For instance, many airports are implementing preconditioned air (PCA) and 400-hz power at the gates. This type of project is designed to reduce the use of APUs on aircraft, by enabling the air- craft power needs when parked at the gate to be met with ground power. Although some 400-hz/PCA projects are funded and implemented by the tenants, others are under- 10 An important point in developing an emissions inventory is to collect sufficient data to enable different equivalency methods and more ad- vanced analyses to be conducted because there is currently no perfect equivalency metric. Within Appendix D, several equivalency methods (radia- tive forcing index [RFI], GWP, global temperature potential [GTP], and others) are reviewed. The appendix describes the underlying assumptions, strengths and weaknesses, and es- timation methods. Although there are differing opinions about the relative usefulness of these different equivalency methods, it is recommended that the latest data from the IPCC Fourth Assessment Report (IPCC 2007) be used. How- ever, as was noted in prior sections, many of the publicly available protocols advocate the use of the IPCC Second As- sessment Report or Third Assessment Report. Although the Fourth Assessment Report represents the state-of-the-art un- derstanding, the international approach to local-level in- ventories has evolved using older data through the protocols developed by TCR, CCAR, and ICLEI. Therefore, for con- sistency with previous inventories, GWPs from the second and third reports could be used if the airport inventory is to be integrated into an inventory that uses these earlier as- sessments. The specific GWPs used should be specified as part of the overall inventory documentation. Consistent with the IPCC Fourth Assessment Report, this Guideline recommends the GWP as the primary means of es- tablishing equivalency for long-lived GHGs; however, in Ap- pendix D, the Guideline notes the many shortcomings associ- ated with the use of GWPs. Further, consistent with the IPCC, the GWP is not recommended for all climate change pollu- tants and impacts. For some short-lived climate change pol- lutants and impacts, the science is either too premature or too physically and chemically complex to support their inclusion in these simplified equivalency methods. This is especially true for some cruise-level effects of airplane emissions (indirect ef- fects of NOx emissions, contrails, and aviation-induced cirrus cloudiness) for which the scientific understanding is not suf- ficiently mature to enable equivalency metrics to be used with confidence. For these situations, more complex computer simulations, exercised over a range of scientific and economic

taken by the airport operator. Further, in many airport set- tings, the electrical demands of the terminal (including the gates) are procured by the airport operator. For those loca- tions where the ground power system is funded by the air- port operator, or where the airport operator pays for the electrical power, the accounting for emissions associated with this need has been transferred from the tenant (due to the reduced reliance on the APU) to the airport operator (where the energy need is then electrical based). Other ex- amples where similar accounting needs may arise include the following: • Airport infrastructure projects—These projects, such as new runways or runway extensions are owned by the airport operator, may be funded through federal grant monies or locally backed revenue bonds, but result in emission reduc- tion changes associated with airport tenants. • National or regional airspace improvement—Delays in cer- tain regions of the country often result in ground holds at cities with air service to those regions. Control of the national airspace and the aircraft that use it rests with the federal government. • Surface traffic improvements—Improvements such as ex- tending regional light rail systems to the airport or airport- sponsored busing programs (such as the Los Angeles’ Van Nuys FlyAway) are designed to increase the use of higher- occupancy vehicles accessing airports versus reliance on single occupancy vehicles. Such programs decrease emis- sions from publicly owned vehicles. There may be merit to developing a separate methodology to allocate recognition or “credit” for emission reductions. Such a methodology is currently outside the scope of this Guidebook. 11 A separate methodology may need to allocate recognition for emissions reductions that cross over between a party that owns and controls the emissions and parties that influence the emissions. We note that in the reporting protocol established by the Global Reporting Initiative (GRI), there is the recognition of emissions owned and controlled by one party where a sub- stantial influence is exerted by another party on the emissions of those sources. Although GRI has not developed an account- ing protocol for such influences, their sustainability plans rec- ognize the influence that various parties may have over another party’s activities (GRI 2008).

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TRB’s Airport Cooperative Research Program (ACRP) Report 11: Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories explores a framework for identifying and quantifying specific components of airport contributions to greenhouse gas emissions (GHG). The report is designed to help airport operators and others to prepare an airport-specific inventory of greenhouse gas emissions.

Appendices A through F to ACRP Report 11 were published online as ACRP Web-Only Document 2. The appendices titles are as follows:

Appendix A-Reasons for Developing GHG Inventories

Appendix B-Emissions and Sources

Appendix C-Methods for Calculating GHG Emissions

Appendix D-Methods for Calculating CO2 Equivalencies

Appendix E-Inventory Development Protocols

Appendix F-Approaches Used in Airport Inventories Prepared to Date

An ACRP Impacts on Practice related to ACRP Report 11 is available.

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